Various types of biometric systems are used more and more in order to provide an increased security for accessing an electronic device and at the same time keep the user convenience at an acceptable level. In particular fingerprint sensors have been successfully integrated in such devices, for example, thanks to their small form factor, high performance and user acceptance. Among the various available fingerprint sensing principles (such as capacitive, optical, thermal etc.), capacitive sensing is most commonly used, in particular in applications where size and power consumption are important.
All capacitive fingerprint sensors provide an indicative measure of the capacitance between several sensing elements and a finger placed on the surface of the fingerprint sensor. Acquisition of a fingerprint image is typically performed using a fingerprint sensor comprising a plurality of sensing elements arranged in a two-dimensional manner, and a block based technique may be applied to the fingerprint sensor for acquiring a fingerprint image, where the blocks of sensing elements are sampled sequentially.
One of the problems associated with fingerprint sensors concerns so-called spoof fingers trying to mimic a live fingerprint to thereby deceive a fingerprint sensor. If fraud by the spoof finger is successful, unauthorized access to systems may undesirably be approved or unauthorized transactions may be approved which may lead to disastrous consequences. Furthermore, a spoof finger is relatively easy to produce which may eventually lead to an increasing number of fraud attempts, in particular as fingerprint sensors become more and more common as a means for authentication.
Therefore, there is a need for improvement with regards to increasing the level of security with regard to authentication with fingerprint sensors.